“School of Rock” had some stars acting like randy school kids on opening night.

Spies said one of the hit musical’s actors spent the Hard Rock afterparty making out with an actress from the original film — and celebrity guests were in a flirtatious mood, too.

A spy at the party told Page Six that Spencer Moses — who plays nerdy Ned Schneebly in the show — “was sitting outside the party on a hydrant with a girl on his lap and his tongue down her throat.”

Another eagle-eyed source said the mystery woman was Becca Brown, who played adorable bassist Katie in the original 2003 Richard Linklater movie.

She’s now a 20-something, self-described “strummin’ songbird” and “comedian.”

“I haven’t seen anybody going at it like that in quite a while,” said the witness of the makeout session. “I didn’t think of Spencer as a big Romeo.”

Brown posted a cute pic on Instagram of the pair. But Moses wouldn’t kiss and tell when asked for comment, saying in a statement: “We were just having fun, or, as the kids backstage call it, ‘playing doctor.’”

At the show, LuAnn de Lesseps and Laverne Cox spent intermission “closerthanthis,” a spy emailed. But a pal explained: “LuAnn loves to flirt. She was flirting with Laverne’s talent because she loves her show. LuAnn was there with a significant, distinguished date. She seems to have a man in her life.”